Rhubarb chia lattice tart

1.Preheat oven to 180°C/350°F. Grease a 25.5cm (10¼in) round, 6cm (2½in) deep fluted, loose-based tart tin.

2.Make vanilla and spice chia pastry.

3.Place reserved vanilla pods on a small oven tray; bake for 25 minutes or until dried. Process dried vanilla pods in a spice grinder to a fine powder.

4.Roll larger portion of pastry between sheets of baking paper until 3mm (¹⁄8in) thick. Lift pastry into tin; ease into side, trim edge. Prick base all over with a fork. Place tin on an oven tray; line pastry with baking paper, fill with dried beans or rice. Bake for 25 minutes or until edges are crisp and base is half cooked. Carefully remove paper and beans; bake for a further 6 minutes or until pastry is browned lightly and crisp. Cool.

5.Meanwhile, place rhubarb, sugar, chia, the water and vanilla bean powder in a large, heavy-based saucepan over high heat, stirring well; cook, covered, for 10 minutes. Reduce heat to medium; cook, uncovered, for a further 30 minutes or until rhubarb is soft and pulpy. Cool to room temperature; transfer to a bowl. Refrigerate until cooled.

6.Roll remaining pastry between sheets of baking paper into a rectangle 25cm x 35cm (10in x 14in). Using a ruler and a sharp knife, cut 12 x 2cm (¾in) wide, 25cm (10in) long strips. Spoon rhubarb filling into tart case (it will reach just to the top). Place pastry strips in a lattice pattern over filling, trimming to fit. Sprinkle with demerara sugar.

7.Pound chia seeds with a mortar and pestle (or grind in a spice grinder) until finely ground. Combine ground chia and the water in a small jug; stand for 30 minutes. Split vanilla beans lengthways; scrape seeds from pods, using the tip of a small knife. Reserve pods to use in step 3. Process flour, sugar, salt, vanilla seeds and mixed spice until well combined; add chia mixture, oil and enough of the soda water until ingredients just come together to form a moist crumble. Turn dough onto a work surface; knead lightly until smooth. Divide dough into two-third and one-third portions, form each into a disc; wrap in plastic wrap. Refrigerate for 30 minutes.